select _blog.id, count(_comment.id)
from _comment
left join _blog
    on _comment.path <@ _blog.path
where extract (day from localtimestamp-_comment.date_publishing) < 30
group by _blog.id

QUERY PLAN                                                                  
---------------------------------------------------------------------------------------------------------------------------------
 GroupAggregate  (cost=1271138177.25..1274205098.25 rows=245483 width=16)
   ->  Sort  (cost=1271138177.25..1272159461.41 rows=408513661 width=16)
         Sort Key: _blog.id
         ->  Nested Loop Left Join  (cost=5.86..1177206898.28 rows=408513661 width=16)
               ->  Seq Scan on _comment  (cost=0.00..452365.30 rows=1664122 width=40)
                     Filter: (date_part('day'::text, (('now'::text)::timestamp without time zone - date_publishing)) < 30::double precision)
               ->  Bitmap Heap Scan on _blog  (cost=5.86..704.07 rows=245 width=40)
                     Recheck Cond: ("outer".path <@ _blog.path)
                     ->  Bitmap Index Scan on gist_idx_blog_path  (cost=0.00..5.86 rows=245 width=0)
                           Index Cond: ("outer".path <@ _blog.path)
(10 rows)